Inter- and intrainstitutional evaluation of automated volumetric capillary cytometry for the quantitation of CD4- and CD8-positive T lymphocytes in the peripheral blood of persons infected with human immunodeficiency virus

Volumetric capillary cytometry (VCC) is a new technology that involves the detection and enumeration of dually fluorochrome-labeled cells in a precise volume. We compared the accuracy and precision of VCC with the accuracy and precision of flow cytometry and hematology (FandH) for the measurement of the absolute numbers of CD4 and CD8 T cells in the whole blood of patients infected with human immunodeficiency virus. Five laboratories, each with a different FandH system and certified by the National Institute of Allergy and Infectious Diseases flow cytometry proficiency testing program, were shipped aliquots of the same samples from a central site in addition to procuring samples locally. In general, the VCC technology generated CD4 and CD8 T-cell counts which were lower than those obtained with FandH. Intralaboratory variability of replicate CD4 T-cell determinations was similar for both technologies except in the local samples with CD4 counts less than 200/μl, where the VCC variability was higher than the FandH variability. Interlaboratory variability on replicate CD4 T-cell counts made by VCC was significantly less than that when counts were made by FandH. The VCC instrument has automated CD4 and CD8 T-cell enumeration in whole blood and has consolidated the process to a single platform. Its performance in this evaluation indicates that it may represent a viable alternative to FandH for obtaining absolute T-cell subset counts.